User Guide

Control system parts
157
Chebyshev filters
The Chebyshev filters allow filtering of the signal based
on a set of frequency characteristics. The output of a
Chebyshev filter depends upon the analysis being
performed.
Note
PSpice computes the impulse response of each Chebyshev filter
used in a transient analysis during circuit read-in. This may require
considerable computing time. A message is displayed on your
screen indicating that the computation is in progress.
For DC and bias point, the output is simply the DC
response of the filter. For AC analysis, the output for each
frequency is the filter response at that frequency. For
transient analysis, the output is then the convolution of
the past values of the input with the impulse response of
the filter. These rules follow the standard method of using
Fourier transforms.
Note
To obtain a listing of the filter Laplace coefficients for each stage,
choose Setup from the Analysis menu, click on Options, and enable
LIST in the Options dialog box.
Each of the Chebyshev filter parts is described in the
following pages.
LOPASS
The LOPASS part is characterized by two cutoff
frequencies that delineate the boundaries of the filter pass
band and stop band. The attenuation values, RIPPLE and
STOP, define the maximum allowable attenuation in the
pass band, and the minimum required attenuation in the
stop band, respectively. The LOPASS part provides one
input and one output.
Figure 35 shows an example of a LOPASS filter device.
The filter provides a pass band cutoff of 800 Hz and a stop
FS stop band frequency
FP pass band frequency
RIPPLE pass band ripple in dB
STOP stop band attenuation in dB
OrCAD Capture recommen
d
s
l
oo
k
ing at one
or more of the references cited in
Frequency-domain device
models on page 6-181
, as well as
some of the following references on analog
filter design:
1 Ghavsi, M.S. & Laker, K.R.,
Modern
Filter Design
, Prentice-Hall, 1981.
2 Gregorian, R. & Temes, G.,
Analog
MOS Integrated Circuits
,
Wiley-Interscience, 1986.
3 Johnson, David E.,
Introduction to
Filter Theory
, Prentice-Hall, 1976.
4 Lindquist, Claude S.,
Active Network
Design with Signal Filtering
Applications
, Steward & Sons, 1977.
5 Stephenson, F.W. (ed),
RC Active Filter
Design Handbook
, Wiley, 1985.
6 Van Valkenburg, M.E.,
Analog Filter
Design
, Holt, Rinehart & Winston,
1982.
7 Williams, A.B.,
Electronic Filter Design
Handbook
, McGraw-Hill, 1981.
Figure 35
LOPASS filter example.
Pspug.book Page 157 Wednesday, November 11, 1998 1:14 PM